Lesson Plan G2 Activity Part Two • Student worksheets The Stars • Pens or pencils Activity Part Three • 1 small flashlight Introduction • 1 large and bright flashlight • A room that can be darkened We see the stars as tiny points of light in the sky. They may all look the same but they are not. They range in size, color, temperature, power, and Time Required life spans. Hands-on Activity Part One: 10 minutes In these hands-on and Starry Night computer Hands-on Activity Part Two: 30 minutes exercises, your students will explore the nature Hands-on Activity Part Three: 10 minutes of stars. They will see how different from one Starry Night Computer Exercise: 35-45 minutes another individual stars can be. They will observe a glowing body as it changes tempera- ture and color. Your students will plot some Conceptual Background properties of stars and learn how these different properties of stars are related to one another All stars form from cold clouds of hydrogen gas and to the mass of the star. They will learn that that collapse under their own gravity. The center the apparent visual brightness of a star is not a of the cloud heats up from the resulting increase good indicator of its distance. In Starry Night in pressure and friction. Eventually the heat and they will examine several different stars and pressure are great enough to force hydrogen they will see how some stars end their lives. nuclei to fuse together and form helium nuclei. This nuclear fusion process releases energy and the star shines with its own light. Key Concepts Stars are made of mostly hydrogen, which is Stars are born, evolve and die. the most abundant element in the universe. Stars Stars have a life cycle that depends on the use hydrogen as a building block to make heavier initial mass of the star. elements. As a star ages it fuses hydrogen into The composition and structure of stars helium, and later the helium will be fused into changes at different stages in their life cycle. a series of increasingly heavier elements. As Stars in the Milky Way can be different from the stars age and continue the fusion process, the Sun in size, temperature, age and brightness. percentage of hydrogen in the stars decreases The Sun is a main sequence star. and the percentage of other heavier elements Stars can be described as having apparent increases. The heaviest elements are fused in magnitude, absolute magnitude and luminosity. the most massive stars. This planet and all that it Other planets orbit around other stars. contains, plus other planets in the solar system Elements heavier than lithium are created in and around other stars, comes from the star-for- the cores of stars. mation process.
Most of the characteristics of a star are gov- Materials Required erned by how much mass the star contains when it first forms. Low mass stars survive for Activity Part One billions of years. They burn their fuel slowly • Small lamp with a clear (not frosted) bulb and at low temperatures. They die a quiet death • Electrical socket with a dimmer switch and leave behind a small white dwarf star that (rheostat) slowly cools into a black dwarf.
www.starrynight.com G2.1 Starry Night High School High mass stars only survive for a few million years. They burn their fuel at extremely high temperatures and rates. Big stars die in spectacular supernova explosions. The supernova can leave behind either a neutron star or a black hole. Electrical Outlet Even in a telescope, stars are so far away that Lamp with they look like tiny points of light. But stars come unfrosted bulb. in a range of sizes, colors, temperatures, energy outputs, and life spans. Most stars are small, dim, red, and cool. They are so small and dim that we can’t see them. When we look into the night sky we see mostly the big, hot, and bright stars.
We think of the Sun as an average star. But if we look at all the stars in the Milky Way galaxy, Rheostat we find that 90 per cent of them are smaller, (Dimmer switch) dimmer and cooler than the Sun. So, although the Sun fits in the middle of the range of stellar properties, it is bigger, brighter and more powerful than most of the stars in our galaxy.
Activity Part One Figure G2.1 Set up to demonstrate the relationship between color and temperature. Stars are hot, glowing objects. This activity is a simple demonstration that shows the relationship between the temperature and color of another hot, glowing object. Our Earth-based experiences often give us the idea that blue is cool or cold, Activity Part One and red is hot, as in “red hot.” With stars, the Discussion Questions opposite is true. It’s all a matter of scale. A. When the lamp is turned down very low, 1. Set up the lamp with the clear, unfrosted what color is the filament in the bulb? bulb so all the students can easily see it. B. When the lamp is turned on full power, is 2. Plug the lamp into a rheostat or an electrical the filament hotter or cooler than when it outlet that is connected to a dimmer is turned down low? switch. C. What color is the filament when the lamp 3. Darken the room. is turned on at full power?
4. Turn on the lamp and dim it until it is just D. What progression of colors did you observe barely on. as the lamp was turned from minimum power up through full power? 5. Ask the students to observe and note the color of the glowing filament in the bulb. E. At what power level did the lamp glow most brightly? Why? 6. Slowly turn up the bulb so it gets brighter and brighter (hotter and hotter). Many students think of something very hot as 7. Have the students observe and note the being “red hot.” They seldom think of blue as changing color of the glowing lamp filament. being a “hot” color. With the lamp turned down to a minimum, the filament glows a dim red
Starry Night High School G2.2 www.starrynight.com color. The filament glows because it is hot, but it Activity Part Two can get much hotter and glow much more brightly. This is a graphing activity that shows the rela- As the lamp is turned up the filament receives tionship between color, temperature and mass more power. It gets hotter and glows brighter. in stars. Table G2a Star Comparison Chart Its color progresses from dim red to orange to gives data for 12 stars. yellow to white. As it gets hotter it glows brighter. There is a relationship between the Your students will use this data to make a temperature and the color of the glowing fila- Hertzsprung-Russell (H-R) diagram that plots ment. If the filament could be made to glow star color versus temperature. A clear relation- even hotter, it would progress from white to ship will emerge. Astronomers call this curve blue in color. At even higher temperatures it on the graph the main sequence. The main would glow with invisible ultraviolet light. sequence is where stars spend most of their lifetimes. Main sequence stars are powered by Most students have seen this color progression hydrogen fusion. from red through yellow to blue in the flame of a propane torch or a propane camp stove. The As you examine the data in Table G2a, you will cool flame is red or orange and the hottest notice a pattern that follows through, more or flame is blue. The same color progression holds less, in descending order, for color, temperature, true for the stars. The coolest stars at 3,000 mass and power. degrees Celsius glow red. The hottest stars have surface temperatures in the tens of thousands of The students’ plots should look similar to the degrees and they glow with a fierce blue light. one shown in figure G2.2. Such stars are extremely bright, powerful, and easy to see from great distances. Much of their radiation is in the form of energetic ultraviolet, X-ray and gamma radiation.
Table G2a Star Comparison Chart
Star Color Temperature in Mass in terms Power in Radius in terms Distance in degrees Celsius of solar mass Suns of Solar Radii Light Years
Sun Yellow 5,700 1 1 1 8 light min. Proxima Centauri Red 2,300 0.1 Unknown Unknown 4 Barnard’s Star Red 3,000 0.1 0.01 0.2 6 Epsilon Eridani Orange 4,600 0.1 0.4 0.8 11 Alpha Centauri Yellow 6,000 1 2 1.4 4 Altair White 8,000 3 12 2 17 Vega White 9,900 3 61 3.3 25 Sirius White 10,000 3 27 2 8.6 Rigel White 10,000 3 52,000 92 777 Regulus White 11,000 8 221 4.3 78 Hadar Blue 25,500 20 79,000 24 526 Alnilam Blue 27,000 20 112,000 44 1,360
www.starrynight.com G2.3 Starry Night High School 1. Give each student a Hertzsprung-Russell D. Look carefully at the data in table G2a. Can diagram worksheet. you see a relationship between power, color and temperature? 2. Use the data from Table G2a to plot each of the 12 stars on the H-R diagram. Star E. Where does the Sun fit into the pattern? color is on the horizontal axis and star temperature is on the vertical axis. Stars come in different sizes and they produce 3. Label each star’s data point with the name different amounts of energy. The energy a star of the star. produces is related to its temperature and color. White and blue stars burn their fuel at the highest 4. Draw a curve as best you can that joins the temperatures. They produce the most energy, data points smoothly. and are the most powerful and most luminous stars. These stars are also the most massive stars. 5. On the outer vertical axis labeled “Mass in Solar Masses” mark the value of each Mass is everything to a star. More mass means star’s mass in terms of solar mass. more self-gravity so the star presses in on itself more strongly. This means it gets hotter in the core than a smaller star, so it burns faster and at a much higher temperature. Because it burns Activity Part Two hotter it also gives off more energy than a Discussion Questions smaller, cooler star.
A. Is there a relationship between the color and The Sun fits in the middle of the range of stellar temperature of a star? properties. It is a yellow star. Compared to other stars, it is neither very hot nor very cool. It is B. What is the relationship between color and neither very massive nor very powerful. Because temperature? of this we think of the Sun as an average star.
C. Generally speaking, are the most massive stars also the hottest?
20 30,000
Alnilam
Hadar 24,000
18,000
12,000 Regulus 8 Rigel Sirius 3 Vega Altair 1 Alpha Centauri 6,000 Sun 0.1 Epsilon Eridani
Mass in Solar Masses in Degrees Celsius Temperature Barnard’s Star 0 Proxima Centauri 0 Blue White Yellow Orange Red
Figure G2.2 Your students’ star plots should look similar to this illustration.
Starry Night High School G2.4 www.starrynight.com Activity Part Three Activity Part Three Discussion Questions The thing we notice first about stars is that some are brighter or dimmer. It looks as though A. If you didn’t know which flashlight was the brighter ones are closer to us and the dimmer which, would you be able to tell which one ones are further away from us. We have just produced the most light? learned that stars vary a lot in the energy, and therefore the amount of light, they produce. B. From this exercise, and the data in table G2a, what conclusion can you draw about This is a simple demonstration activity to prove the stars Rigel and Sirius? that the apparent brightness of a star cannot be used to judge its distance. This is one of the most fundamental questions 1. Place the small flashlight on a desk or table about the stars. Is it bright because it is close, near the front of the room. or is it bright because it is intrinsically bright? This is why astronomers must know the dis- 2. Place the large flashlight on a desk or table tance to a star. Without knowing the distance, near the back of the room. it’s hard to get meaningful information about the other properties of the star. Some stars look 3. Have the students gather at the front of the bright because they are very near the Sun. Others room so they can all see both flashlights look equally bright but are many times further easily. away from the Sun. These more distant stars are extraordinarily bright. Without knowing the 4. Turn on both flashlights. distance it’s impossible to distinguish between the two. 5. Darken the room. The two flashlights can be compared to the stars 6. Observe and compare the apparent Sirius and Rigel. Sirius is about twice as bright brightness of the two flashlights. as Rigel, but Rigel is almost 100 times further away than Sirius. Sirius is about 27 times as 7. Move the two flashlights back and forth powerful as the Sun, but Rigel has the power of until they both appear to have the same many thousands of Suns. Sirius looks very bright brightness. because it is close. If Rigel were as close as Sirius it would be blindingly bright.
Large Flashlight Small Flashlight Observer Far from observer the large Close to observer small flashlight looks dimmer flashlight looks brighter than small flashlight than the large flashlight.
Figure G2.3 Two flashlights of different power placed at different distances can be used to demonstrate that apparent brightness is not a good indicator of distance. www.starrynight.com G2.5 Starry Night High School Starry Night Computer Exercise Lesson G2: The Stars
Even a cursory examination of the night sky shows Stellar evolution is a complex subject but students that not all stars are the same -- some are brighter, should be able to understand that in general, hot some are fainter. A more careful inspection will show bluish stars are young, yellowish stars are middle-aged that star colors are not the same. But the difference is and large reddish stars are near the end of their life. subtle. Astronomers can deduce a lot of information about stars from their properties. This exercise examines some Students might be interested in using the interactive of these. H-R diagram on other stars. The status pane can be used whenever catalogued stars are visible in the main Teaching Strategies window. (Some stars do not have sufficient data to be plotted on the H-R diagram) Students should be aware that all values entered in the database are approximate and subject to errors. If a small telescope is available, it is strongly suggested Indeed, different sources will give different values for that observations of some colorful stars like Albireo be most of the parameters. attempted.
Colors are difficult to detect and have been exaggerated Students can be expected to complete this exercise in in Starry Night. If a more realistic appearance is desired, 35 to 45 minutes. see Using Starry Night in the Appendix of this binder on how to change color saturation.
Conclusion Lesson Specific Resources
Stars are not simple points of light. After SkyGuide completing these activities and exercises, Guided Tours>Our Solar System, the Stars and students should know that stars have a range Galaxies> The Stars of properties. They should understand that the Guided Tours>Our Solar System, the Stars and color, temperature and mass of a star are inter- Galaxies> Nebulae related. Students should know that the mass of a star governs everything about the star. Students Guided Tours>Our Solar System, the Stars and should know the apparent brightness of a star Galaxies> Novas and Supernovas cannot be used to judge its distance.
Starry Night High School G2.6 www.starrynight.com Lesson Plan G2 The Stars Student Worksheet: Hertzsprung-Russell Diagram
Table G2a Star Comparison Chart Use the information in this table to help build your own H-R diagram.
Star Color Temperature in Mass in terms Power in Radius in terms Distance in degrees Celsius of solar mass Suns of Solar Radii Light Years
Sun Yellow 5,700 1 1 1 8 light min. Proxima Centauri Red 2,300 0.1 Unknown Unknown 4 Barnard’s Star Red 3,000 0.1 0.01 0.2 6 Epsilon Eridani Orange 4,600 0.1 0.4 0.8 11 Alpha Centauri Yellow 6,000 1 2 1.4 4 Altair White 8,000 3 12 2 17 Vega White 9,900 3 61 3.3 25 Sirius White 10,000 3 27 2 8.6 Rigel White 10,000 3 52,000 92 777 Regulus White 11,000 8 221 4.3 78 Hadar Blue 25,500 20 79,000 24 526 Alnilam Blue 27,000 20 112,000 44 1,360
20 30,000
24,000
18,000
8 12,000 3
1 6,000 0.1 Mass in Solar Masses in Degrees Celsius Temperature 0 0 Blue White Yellow Orange Red
www.starrynight.com G2.7 Starry Night High School Starry Night Computer Exercises Name: Lesson G2: The Stars Class:
Instructions for the Student
Click on the SkyGuide pane, choose Student Exercises > G – Stars > G2: The Stars and follow the instructions given. Record your answers to the questions in the spaces provided. Leave the last column blank for now.
Right click on each star and choose “Show Info” from the menu. Under the headings “Position in Space” and “Other Data” you will find all the information you need to complete the chart.
Star Database
Star Color Distance Radius Apparent Temperature Luminosity from Sun in compared magnitude in Kelvins light years to Sun
Sirius
Aldebaran
Pollux
Capella
Procyon
Orange
Return to SkyGuide to complete the rest of the exercise.
Question 1: Colorful stars a) Do all stars have approximately the same temperature? Explain.
b) What seems to be the color of stars that have a temperature in the 3000’s degrees?
Continued next page
Starry Night High School G2.8 www.starrynight.com Lesson G2: The Stars c) Pick any other orange star in the main window and enter its name and temperature in the table. Was your prediction in b) correct?
d) Are all stars about the same size?
e) Do stars always appear brighter when they’re closer to us? Explain.
f) Do bigger stars always appear brighter to us? Explain.
Question 2: In the beginning
Why are stars born in a nebula?
Question 3: Going out gently
Why is the central star of the nebula difficult to see?
Question 4: Going out with a bang
The Crab Nebula requires a telescope to see. Telescopes were not invented until the 1600’s. How could the supernova have been seen in 1054?
Continued next page www.starrynight.com G2.9 Starry Night High School Lesson G2: The Stars
Question 5: The H-R Diagram
All the stars shown in the main window are plotted on the H-R diagram. Point to any star in the main window and a red dot will show its position on the H-R diagram. Go ahead, try it! a) Now let’s fill in the last column on your Star Database. Record to what group each star in your database belongs. (i.e. red giant, main sequence etc) b) To what group do you think the star Rigel belongs? (Hint: read the introduction carefully)
Return to SkyGuide to complete the Extra Credit for this exercise.
Extra Credit a) What appear to be the colors of Albireo and its companion?
b) What do the colors of these two stars tell us about their surface temperatures?
c) How would you find Albireo in the summer sky?
Starry Night High School G2.10 www.starrynight.com